1. Field of the Invention
This invention relates to the repair of frangible items, and in particular to a cast-in-place repair of transparent and translucent items adapted to transmit diffused light, such as automobile lenses of the kind used over turn signal lights and brake lights, and commercial signs displayed to advertise businesses.
2. Description of Prior Art
Broken plastic articles have long been repaired by glueing the broken pieces together with a hardening, adhering compound. Normally this function is accomplished by applying glue to the edges of a broken area, matching the broken piece to the area from which it came, and then applying pressure. A broken lens can be thus repaired by building it up as a jigsaw puzzle, using the broken parts.
Unfortunately, many frangible items, including signal light lenses, are sufficiently brittle to shatter, but are also resilient such that stresses forming as the article is broken cause broken pieces to fly off. It is therefore usually the case that all the parts of the "jigsaw puzzle" are not available to be glued together. In addition, the plastic material of a sign or tail light is subject to deformation before breaking. Therefore, even if all the pieces can be found, they will not necessarily fit together again, because some may have been substantially deformed before and during breaking. A simple glue applied to directly join the broken pieces together is therefore inadequate.
In breaking, a plastic lens will exhibit a number of features. Pieces which are broken away or lost will leave holes, and chipped away depressions will remain on either or both of the inner and outer surfaces of the broken lens adjacent holes and cracks. Such chipped-out depressions are usually located at the junctions of cracks. The cracks radiate from a hole at the point of impact, or from some other nearby stress point, in a sunburst or spoked pattern.
The prior art has conceived of fixing articles having an open hole by filling the hole with a moldable material. With respect, for example, to rusted or dented automobile bodies, viscous moldable material is simply placed into the open hole or depression, and is allowed to cure and harden. The hole is usually overfilled, and after curing, the surface is sanded or otherwise treated as desired to approximate the undamaged contour. In filling a completely open void of substantial size, the material must be applied in stages, allowing previous stages to harden in order to support subsequent stages. The prior art alternatively employs screen-like material to bridge any substantial gap and prevent the moldable material from merely falling through the open hole which it is intended to close. Material falling through the hole is, of course, wasted. Material placed to extend past the undamaged contour is also wasted and must be removed without damaging and scratching adjacent undamaged areas. Wherever it is placed, filler material allowed to harden can be difficult to remove. In the enviroment of transparent or translucent lenses or covers, a screen or such hole-bridging member would prevent filler loss but is impractical in that it noticeably blocks light. Nevertheless, it is important to prevent the moldable hole-filling material from simply falling through the repaired hole.
The damage resulting from impact on a plastic lens such as an automobile tail light lens usually exceeds open holes exclusively. Cracks radiate from the point of impact, and chipping may occur on either or both of the inner and outer surface, usually adjacent the cracks. It is exceedingly difficult, if not impossible to adequately fill narrow cracks and chipped surfaces with the usual viscous moldable material. The moldable material is simply too thick to smoothly force into narrow spaces. In addition, as cracks, chips and surface checking may occur on either the inner or outer face, or both, the thick moldable material must be separately applied to each face, in order to fill in cracks.
In order to avoid the necessity of applying viscous moldable material to both an inner and outer surface of a broken article, the prior art has attempted to employ curable liquids, applied under pressure to cause the liquid to flow into all areas of the break. Heating apparatus have been used to generate elevated temperature and speed curing. A typical cosmetic repair is accomplished by applying curable liquid to a damaged automobile windshield using temperature and pressure. A cup-shaped body is placed over the damaged area in order to confine the pressure and presumably to urge the liquid compound into the damaged area.
The present invention employs a curable liquid resin which cures by exothermic chemical reaction, tending to open the cracks and facilitating flow of the resin along and into the cracks due to decreased viscosity caused by the increased temperature. Accordingly, an external source of pressure is not strictly necessary. The material is self-leveling and will seek the lowest level, flowing outward into any cracks where it is placed in uncured state. A casting form is employed to restrict flow past a certain surface, namely, that of the undamaged contour. The resin is preferably matched in color and light transmission properties to the plastic or other material to which it will be adhered, by suitable dyeing, whereby it will be indistinguishable from the balance of material.
When applied, the curable material of the invention is confined to the open areas of a broken article by means of a casting form coated with a release agent and placed on the flat external surface of the article. The casting form causes the material to cure in the desired external shape, and restricts flow. The material therefore flows outwards from a puddle on the form at the point of application, to fill the cracks, crevices and chipped areas. The invention provides a means of repairing broken articles such as plastic tail lights and the like, by which the repaired area is virtually indistinguishable from the remainder of the article.